The Student Room Group

why does negative*negative=positive?

yh

Scroll to see replies

Any complex number can be written in the form re^i(theta), for negative numbers theta = (2n+1)pi (r is the (positive) magnitude of the negative number)
When you multiply two numbers:
re^i(2n+1)pi*se^i(2m+1)pi = rse^i(2n+2m +2)pi = rse^i(2k)pi
e^ik(2pi) = 1
therefore = rs*1 = rs
no negative sign any more
Reply 2
Original post by ValerieKR
Any complex number can be written in the form re^i(theta), for negative numbers theta = (2n+1)pi (r is the (positive) magnitude of the negative number)
When you multiply two numbers:
re^i(2n+1)pi*se^i(2m+1)pi = rse^i(2n+2m +2)pi = rse^i(2k)pi
e^ik(2pi) = 1
therefore = rs*1 = rs
no negative sign any more

i still dont understand
Original post by p29
i still dont understand


uh... because maths
Reply 4
Original post by ValerieKR
uh... because maths

lel.
Reply 5
I think about it this way: Loss of a loss is a gain.
negative * negative is, in a very loose way, loss of a loss.
Reply 6
Original post by ValerieKR
Any complex number can be written in the form re^i(theta), for negative numbers theta = (2n+1)pi (r is the (positive) magnitude of the negative number)
When you multiply two numbers:
re^i(2n+1)pi*se^i(2m+1)pi = rse^i(2n+2m +2)pi = rse^i(2k)pi
e^ik(2pi) = 1
therefore = rs*1 = rs
no negative sign any more


Two words: learn Latex :P
Reply 7
Original post by oShahpo
I think about it this way: Loss of a loss is a gain.
negative * negative is, in a very loose way, loss of a loss.

loss-loss=-loss
Original post by oShahpo
I think about it this way: Loss of a loss is a gain.
negative * negative is, in a very loose way, loss of a loss.


You're thinking of -- =+ rather than (-x)(-y)=xy
Reply 9
Original post by p29
yh


Because two wrongs always make a right
Reply 10
Original post by SGHD26716
Because two wrongs always make a right

y:confused:
Because a double negative = a positive.

'Elephants are grey' = positive
'Elephants are not grey. = negative
Elephants are not not grey.' = double negative = elephants are grey

If something is not not something, then it is that thing. 'Negative' is basically another way of saying 'opposite': imagine the number 2 sees itself in a mirror. The number 2 is 2 units away from zero. The number minus 2 is 2 units away from zero, but in the opposite direction.

So -2*-2 = - - 4, i.e. the opposite of minus 4. The opposite of -4 is 4.
(edited 7 years ago)
Original post by p29
loss-loss=-loss


loss-loss=0
Reply 13
Original post by Copperknickers
Because a double negative = a positive.

'Elephants are grey' = positive
'Elephants are not grey. = negative
Elephants are not not grey.' = double negative = elephants are grey

If something is not not something, then it is that thing. 'Negative' is basically another way of saying 'opposite': imagine the number 2 sees itself in a mirror. The number 2 is 2 units away from zero. The number minus 2 is 2 units away from zero, but in the opposite direction.

So -2*-2 = - - 4, i.e. the opposite of minus 4. The opposite of -4 is 4.

maths=english??
Reply 14
Original post by XOR_
loss-loss=0

house-house=-house
Original post by p29
house-house=-house


house-house=emptyland.
Original post by ValerieKR
You're thinking of -- =+ rather than (-x)(-y)=xy


No I am not. (-2) * (-2) means you lose a loss of 2 twice, which means that you gain 2 twice. Similarly, (2) * (-2) means you gain a loss of two twice, which means you lose 4.
Original post by p29
yh


If I take away three lots of taking away three, I have 9 more than I would if I hadn't taken away three lots of taking away three.
Reply 18
Original post by XOR_
house-house=emptyland.

emptyland=-house
Reply 19
Original post by ValerieKR
If I take away three lots of taking away three, I have 9 more than I would if I hadn't taken away three lots of taking away three.

9 more of what?

Quick Reply

Latest